It is almost 17 years since the death of Massimo Troisi, the star of my film Il Postino, yet he is as present in my life as he was when he lived. There was nothing overtly Neapolitan about him, except for his accent, which was so thick it took me months to understand. That amused him a lot.

Practically his entire life was marked by illness. He'd contracted rheumatic fever, the illness of the poor, when he was young, and it had damaged his heart. After a quadruple bypass when he was 19, he knew that sooner or later he was going to need a heart transplant. He bore it without complaint. But it gave him a profundity at a young age that gave his humour a real meaning.

I got to know him when I made my first film, Another Time, Another Place, which was about three Italian prisoners of war in Scotland. I had seen his first film Ricomincio da Tre (aka I'm Starting From Three) at the London film festival and was immediately struck by his humour. I asked him to be in the film, and he refused because he said Scotland was too cold. When the film came out, he called me up and in his mumbly way told me it was his favourite movie and asked if I would like to collaborate on a movie in Naples. I told him Naples was too hot. We became friends, and for eight years we would meet once or twice a year to discuss various projects – as you do in this business, without much hope of finding anything.

Then we found something – a Chilean novel called A Burning Patience – and went to Los Angeles to adapt it. Il Postino was written in three weeks in Shutters Hotel in Santa Monica, because Massimo wanted to be somewhere people would not recognise him. Occasionally, we would have to visit some famous Italian restaurant where people would stare, and the waiters would ask for his autograph, so he could remind himself he was still famous.

But there was another motive. He wanted to have a medical check in Houston. So I went back to Naples. And there I waited, and waited. I found out later he had been told his heart was the size of a football and he needed a new one. He asked for a temporary operation in order to stabilise his condition and continue with the film. The doctors agreed, and when he came back, he seemed fine.

But he wasn't. On the third day of shooting, he collapsed. He went to stay with his sister, and it seemed the film was over. Three days later he called me. "How was I?" he asked. I knew he wanted me to decide whether he should risk his life. My heart told me yes, my head no. Was I signing his death warrant? I didn't know. But I knew that he had been sensational. So I told him. "OK," he said. "I'm carrying on."

At the end, when I had finished shooting, he told me had an appointment at Harefield hospital for a new heart the following day. Then he said to me: "You know, I don't really want this new heart. You know why? Because the heart is the centre of emotion, and an actor is a man of emotion. Who knows what kind of an actor I'm going to be with someone else's heart beating inside me?"

He never made it: I heard of his death on the radio the next day.

Many people think that the movie ends with the death of the main character because Massimo had died. It was not true. That's how we wrote it. And when Mario Cecchi Gori, the producer, asked if ending with a death was not too depressing, Massimo said: "No, Mario. Because there is no death in the movies."

And he was right.

Il Postino screens, with a Michael Radford Q&A, on 6 April, as part of the Italian film festival at the Riverside Studios, London. Details: italiancinema london.co.uk